Semiconductor device

ABSTRACT

Provided is a method of realizing a semiconductor device having a structure in which a sufficient light shielding property is compatible with a sufficient storage capacitance without reducing an aperture ratio. A lower light shielding film is formed on a substrate, a TFT is formed on the lower light shielding film, and an upper light shielding film is formed on the TFT via an interlayer insulating film to cover and fit the TFT. Thus, the TFT can be completely light-shielded by the lower light shielding film and the upper light shielding film and an occurrence of a photo leak current can be prevented.

This application is a continuation of U.S. application Ser. No.10/152,227, filed on May 21, 2002 now U.S. Pat. No. 6,734,463.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor element typically athin film transistor (TFT), using particularly a crystallinesemiconductor film as a semiconductor layer including a channel formingregion, a source region, and a drain region. Also, the present inventionrelates to a semiconductor device using such a TFT as a driver circuitor a switching element of a pixel (particularly, a liquid crystaldisplay device or a light emitting device) and a manufacturing techniquethereof. Further, the present invention particularly relates to asemiconductor device having a structure in which a light shieldingproperty is improved and a manufacturing technique thereof.

2. Description of the Related Art

In recent years, a liquid crystal projector in which characteristicssuch as miniaturization and weight reduction are improved has been usedin various situations. In response to that, competition of developmentfor providing a liquid crystal projector having a smaller size andlighter weight is intensified. The liquid crystal projector isconstructed so as to project an image and the like displayed on a liquidcrystal display device and the performance of the liquid crystalprojector is greatly influenced by a display quality of the liquidcrystal display device.

As to the liquid crystal display device, the mainstream is one in whichliquid crystal is sealed between a substrate in which a TFT and a pixelelectrode are formed (hereinafter referred to as a TFT substrate) and asubstrate in which a counter electrode is formed (hereinafter referredto as a counter substrate) and an alignment of the liquid crystal iscontrolled by an electric field produced between the pixel electrode andthe counter electrode to display an image.

In recent years, an active matrix type liquid crystal display device(liquid crystal panel) having several million pixels in a pixel portionis greatly used as a liquid crystal display device. In such a liquidcrystal panel, a TFT is provided in each of pixels as a switchingelement for providing a potential to each of pixels and a pixelelectrode is provided in each TFT. When the TFT is turned on, thepotential of the pixel electrode is set. When the TFT is turned off, thepotential of the pixel electrode is kept by charges stored in a storagecapacitor element (hereinafter referred to as a storage capacitor).

When the potential of the pixel electrode is changed while the TFT is inan off state, a display quality is deteriorated. Thus, it is requiredfor an active matrix type TFT substrate that a leak current of the TFTis suppressed, a sufficient storage capacitance is obtained for each ofpixels, and the amount of charges stored in the storage capacitor issufficiently larger than that lost by a leak current.

Also, in the case of a transmission type liquid crystal panel, in orderto increase the intensity, it is necessary to increase an occupyingratio of an opening portion, that is, a region which is intended tocontrol display in a pixel (for example, a region through which light istransmitted and which contributes to display in the case of atransmission type display device, a region from which light is reflectedand which contributes to display in the case of a reflection typedisplay device, a region in which an organic light emitting layersandwiched by electrodes emits light and which contributes to display inthe case of a display device using an organic light emitting element, orthe like).

Incidentally, in the case where the above-mentioned liquid crystal panel(in particular, a transmission type liquid crystal panel) is used for aliquid crystal projector, when light is incident into the semiconductorlayer of a TFT, since a leak current due to photo-excitation(hereinafter referred to as a photo leak current) is caused, it has anadverse affect on display. Thus, a light shielding layer is provided inthe liquid crystal panel. For example, when a light source of theprojector is located in a counter substrate side, the light shieldinglayer is formed between a pixel electrode and a TFT to block light fromthe light source, or the light shielding layer is formed between asubstrate and a semiconductor layer to block light reflected from aprojection lens or the like. Also, according to Japanese PatentApplication Laid-Open No. 2000-164875, a concave portion is provided ina substrate and a lower light shielding film is formed on the entireinner wall surface of the concave portion. Thus, the channel formingregion of a TFT is formed so as to be buried in the concave portion.Also, an upper light shielding film is formed together.

However, according to the structure disclosed in the above publication,unevenness is formed near a TFT on which various wirings areconcentrated. Thus, a possibility of reducing a yield is high because,at the time of wiring formation, a short circuit and a break of wiringsare easily caused, or the wirings are easily deteriorated by theconcentration of an electric field.

Also, according to the structure disclosed in the above publication, agap is present between the upper light shielding film and the lowerlight shielding film. Thus, in the case of such a structure, there isalso a possibility that a photo leak current by stray light is caused.Further, since the concave portion is provided in the substrate, thereis a possibility that the mechanical strength of the substrate isreduced.

In the case of a projector for which a high intensity and a highdefinition are required, first, the intensity of a lamp used as a lightsource is increased to increase a display brightness. Second, the numberof pixels in a panel used for an optical system is increased to obtain ahigher definition. However, in the conventional methods of forming thelight shielding film between the pixel electrode and the TFT and offorming the light shielding film between the substrate and thesemiconductor layer, there is a problem that light diffracted by endportions of the light shielding film is incident into the semiconductorlayer to cause a photo leak current.

Further, with increasing the intensity of the light source, an adverseaffect on the TFT by the diffracted cannot be neglected any longer.

Also, when a thin insulating film is used for isolating the lightshielding film and the TFT, the intensity of the diffracted light in theposition of the TFT call be reduced to a negligible extent. However,when the insulating film is made thinner, a parasitic capacitanceproduced between the TFT and the insulating film is increased.Therefore, a problem occurs in that an operation of the TFT isinfluenced by a potential of the light shielding film.

Also, when a width of the light shielding film is expanded, a problemthat diffracted light is incident into the TFT can be solved. However,it is natural to reduce an aperture ratio. In addition, since therequirement for a high definition of display is satisfied by increasingthe number of pixels, a size of respective pixels is decreased. Thus, areduction in an aperture ratio due to the expansion of the width of thelight shielding film and a reduction in brightness accompanied by such areduction become a large problem.

Also, only when the width of the light shielding film is expanded, aproblem that stray light produced by unintended scattering in aninterlayer insulating film is incident into the TFT (in particular, thesemiconductor layer) cannot be solved. With increasing the intensity ofthe light source as described above, the influence of the stray lightalso cannot be neglected.

Also, in a TFT including an active layer having a crystalline structure,which has been actively used because of its high field effect mobilityand the like, a photo leak current tends to increase as compared with aTFT including an amorphous semiconductor layer. If the TFT have nosufficient storage capacitance, stored charges are decreased by the leakcurrent to change the amount of light to be transmitted, which becomes acause for reducing a contrast in image display. Thus, it is necessary toform a storage capacitor element capable of securing a sufficientcapacitance in a liquid crystal panel.

However, when an area of the storage capacitor is expanded in twodimensions to secure the sufficient capacitance, an occupying ratio ofthe storage capacitor element to an area of a pixel is increased toreduce an aperture ratio.

Further, in order to improve a yield, it is necessary to use a structurein which a break of wiring and the like are not caused by unevenness dueto the presence of the storage capacitor.

SUMMARY OF THE INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and an object of the present invention is to provide a methodof realizing a semiconductor device having a structure in which asufficient light shielding property is compatible with a sufficientstorage capacitance without reducing an aperture ratio.

In order to solve the above problems, the present inventor considered astructure for reducing diffracted light and stray light, which areincident into the semiconductor layer of a TFT by forming a lightshielding film so as to cover and fit the TFT.

FIG. 1A shows one example of a structure of a pixel for which thepresent invention is adopted.

A light shielding film is formed between a pixel electrode and a TFT. Inthis specification, a light shielding film in which at least a portionthereof is formed between the pixel electrode and the TFT is called anupper light shielding film. In the pixel, a groove is formed between aregion through which light is transmitted and for which display iscontrolled and the TFT, and then a conductive film as the upper lightshielding film is formed. It is different from a conventional structurehaving the light shielding film formed between the TFT and the pixelelectrode. That is, the upper light shielding film is continuouslyformed from a region located between the pixel electrode and the TFT toa region through which light is transmitted so that the TFT is coveredand fit with the upper shielding film.

FIG. 1B shows another structure of a TFT for which the present inventionis adopted.

A TFT composed of a semiconductor layer, a gate insulating film, and agate electrode is formed and an interlayer insulating film is formed.After that, the gate insulating film and the interlayer insulating filmin a region through which light is transmitted and for which display iscontrolled in a later stage and its surrounding region are removed. Inthis specification, a hole-shaped region (having a wall surface and abottom surface) is called a window for the sake of simplification, inwhich a portion of the gate insulating film and a portion of theinterlayer insulating film are removed and which has the substantiallysame area as a region (opening portion) intended to control display in adisplay device. The upper light shielding film and the insulating filmare formed in the wall surface of the window. Thus, although the area ofthe opening portion is smaller than that of the window by the filmthickness, it can be said that the area of the window and that of theopening portion are substantially identical to each other.

Here, when the window shown in FIG. 1B is compared with the groove shownin FIG. 1A, since the window has a small aspect ratio, the formation ofthe upper light shielding film is simple and easy. Next, a lightshielding film is continuously formed to cover a region from the top ofthe TFT to the side surface of the window. After that, the lightshielding film formed on the bottom surface of the window (inparticular, a region through which light is transmitted) is removed, andthen an insulating film is formed and the window is filled with atransparent organic resin film made of acrylic or the like for leveling.Next, an insulating film is formed such that the light shielding film isnot in contact with a pixel electrode and then the pixel electrode isformed. Thus, the structure is obtained such that the TFT is covered andfit with the upper light shielding film and the window is formed byremoving the interlayer insulating film and filled with the transparentorganic resin insulating film for leveling.

In the case of the above structure, an area of the region (window) inwhich a portion of the gate insulating film and a portion of theinterlayer insulating film are removed is substantially equal to that ofthe region (opening portion) intended to control display in a pixel. Inaddition, the region (opening portion) intended to control display has asmaller area than that of the region (window) in which at least theportion of the gate insulating film and the portion of the interlayerinsulating film are removed.

FIG. 1C shows another structure of a pixel for which the presentinvention is adopted. In the example shown in FIG. 1C, in order to alsoblock light incident from a substrate side, a light shielding film isformed between the substrate and a semiconductor film before theformation of the semiconductor film. Note that the light shielding filmformed between the substrate and the semiconductor film is hereinaftercalled a lower light shielding film in this specification. Next, a TFTcomposed of a semiconductor layer, a gate insulating film, and a gateelectrode is formed and an interlayer insulating film is formed. Afterthat, the gate insulating film and the interlayer insulating film whichare formed in a region for which display is controlled later and itssurrounding region are removed to form a window. Next, a light shieldingfilm is continuously formed from the top of the TFT to the window. Afterthat, the lower light shielding film formed on the bottom surface of thewindow and the upper light shielding film are removed to form an openingportion (region intended to control display). Next, an insulating filmis formed and the window is filled with a transparent organic resin filmmade of acrylic or the like for leveling. Next, an insulating film isformed such that the light shielding film is not in contact with a pixelelectrode and then the pixel electrode is formed. Thus, the structure isobtained such that the TFT is covered with the upper light shieldingfilm and completely light-shielded by the upper light shielding film andthe lower light shielding film. Note that, if a ground potential isprovided for the upper light shielding film and the lower lightshielding film, the TFT can be electrically shielded.

Further, when a color filter is formed in a counter substrate side,there is a problem that a matching accuracy between the countersubstrate and a TFT substrate is reduced due to a decrease of a pixelsize for high definition display. Thus, a method of forming the colorfilter in a TFT substrate side is considered. However, for theorientation of liquid crystal, it is necessary to form a pixel electrodeafter the formation of the color filter. Here, since the color filterhaving a thickness of 1 μm or larger is required, it is difficult toelectrically connect the pixel electrode and a drain electrode which areisolated by the color filter.

Therefore, in the examples shown in FIGS. 1B and 1C when the window isfilled with a photoresist film colored with R (red), G (green) or B(blue) for leveling, the same function is obtained as in the case of thecolor filter formed in a counter substrate.

Also, although not shown, in the structure shown in FIG. 1B or 1C, theupper light shielding film is made of a material having a highreflectance such as aluminum. In addition, the upper light shieldingfilm on the bottom surface of the region (window) in which at least theportion of the gate insulating film and the portion of the interlayerinsulating film are removed is not removed and is used as a reflectiveplate. In this case, a reflection type display device can be alsoobtained.

According to the present invention, there is provided a semiconductordevice comprising: a substrate; a TFT located over the substrate; apixel electrode electrically connected with the TFT; an upper lightshielding film located between the TFT and the pixel electrode; at leastone interlayer insulating film formed over the TFT; and a window formedbetween the pixel electrode and the substrate by removing the interlayerinsulating film, the semiconductor device being characterized in thatthe upper light shielding film is continuously formed from a bottomsurface of the window to a surface of the interlayer insulating film tocover and fit the TFT, and an area of the window is substantially equalto that of the opening portion.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a lower light shieldingfilm located on the substrate, a TFT located over the lower lightshielding film; a pixel electrode electrically connected with the TFT;an upper light shielding film located between the TFT and the pixelelectrode; at least one interlayer insulating film formed over the TFT;and a window which is formed between the pixel electrode and thesubstrate by removing the interlayer insulating film and provided withan opening portion, the semiconductor device being characterized in thatthe upper light shielding film is continuously formed from a bottomsurface of the window to a surface of the interlayer insulating film tocover and fit the TFT, and an area of the window is substantially equalto that of the opening portion.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a lower light shieldingfilm located on the substrate;

a TFT located over the lower light shielding film; a pixel electrodeelectrically connected with the TFT; an upper light shielding filmlocated between the TFT and the pixel electrode; at least one interlayerinsulating film formed over the TFT; and a window formed between thepixel electrode and the substrate by removing the interlayer insulatingfilm, the semiconductor device being characterized in that the upperlight shielding film is continuously formed from a bottom surface of thewindow to a surface of the interlayer insulating film to cover and fitthe TFT, and the lower light shielding film is in contact with the upperlight shielding film at the bottom surface of the window.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a lower light shieldingfilm located on the substrate; a TFT located over the lower lightshielding film; a storage capacitor element formed in parallel to theTFT; a pixel electrode electrically connected with the TFT; an upperlight shielding film located between the TFT and the pixel electrode; atleast one interlayer insulating film formed over the TFT and the storagecapacitor element; and a window formed between the pixel electrode andthe substrate by removing the interlayer insulating film, thesemiconductor device being characterized in that the lower lightshielding film is in contact with the upper light shielding film at abottom surface of the window.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a TFT located over thesubstrate; a pixel electrode electrically connected with the TFT; alight shielding film located between the TFT and the pixel electrode; atleast one interlayer insulating film formed over the TFT; and a windowformed between the pixel electrode and the substrate by removing theinterlayer insulating film, the semiconductor device being characterizedin that the window is filled with a transparent organic insulating filmfor leveling, and the light shielding film is continuously formed from abottom surface of the window to a surface of the interlayer insulatingfilm to cover and fit the TFT.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a lower light shieldingfilm located on the substrate; a TFT located over the lower lightshielding film; a pixel electrode electrically connected with the TFT; alaminate body which is located between the TFT and the pixel electrodeand provided with a plurality of upper light shielding films and aplurality of insulating films which are alternately laminated; at leastone interlayer insulating film formed over the TFT; and a window formedbetween the pixel electrode and the substrate by removing the interlayerinsulating film, the semiconductor device being characterized in thatthe window is filled with a transparent organic insulating film forleveling, and the plurality of laminated light shielding films areformed from a bottom surface of the window to cover and fit the TFT.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a lower light shieldingfilm located over the substrate; a TFT located on the lower lightshielding film; a pixel electrode electrically connected with the TFT; alaminate body which is located between the TFT and the pixel electrodeand has a plurality of upper light shielding films and a plurality ofinsulating films which are alternately laminated; at least oneinterlayer insulating film formed over the TFT; and a window formedbetween the pixel electrode and the substrate by removing the interlayerinsulating film, the semiconductor device being characterized in thatthe window is filled with a transparent organic insulating film forleveling, the plurality of laminated light shielding films are formedfrom a bottom surface of the window to cover and fit the TFT, and atleast one upper light shielding film of the laminate body iselectrically connected with the TFT and the pixel electrode.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a lower light shieldingfilm located on the substrate; a TFT located over the lower lightshielding film; a pixel electrode electrically connected with the TFT; alaminate body which is located between the TFT and the pixel electrodeand has a plurality of upper light shielding films and a plurality ofinsulating films which are alternately laminated; at least oneinterlayer insulating film formed over the TFT; and a window formedbetween the pixel electrode and the substrate by removing the interlayerinsulating film, the semiconductor device being characterized in thatthe window is filled with a transparent organic insulating film forleveling, the plurality of laminated light shielding films are formedfrom a bottom surface of the window to cover and fit the TFT and astorage capacitor element is formed by the insulating film and theplurality of upper light shielding films which are formed via theinsulating film in the laminate body.

Also, according to the present invention, there is provided asemiconductor device comprising: a substrate; a TFT located over thesubstrate; a pixel electrode electrically connected with the TFT; alaminate body which is located between the TFT and the pixel electrodeand has a plurality of upper light shielding films and a plurality ofinsulating films which are alternately laminated; at least oneinterlayer insulating film formed over the TFT; a window formed betweenthe pixel electrode and the substrate by removing the interlayerinsulating film; and a wiring for electrically connecting the TFT andthe pixel electrode, the wiring being one layer of the upper lightshielding films which are formed from a bottom surface of the window tocover and fit the TFT, the semiconductor device being characterized inthat an area of the window substantially equal to that of a region whichis intended to control display in a pixel.

Also, according to the present invention, there is provided asemiconductor device characterized by further comprising a lower lightshielding film formed between the substrate and the TFT.

Also, according to the present invention, there is provided asemiconductor device characterized in that a first layer of the upperlight shielding layers is in contact with the lower light shielding filmat the bottom surface of the window between the pixel electrode and thesubstrate.

Also, according to the present invention, there is provided asemiconductor device characterized in that the window includes aphotoresist film colored with one of R (red), G (green), and B (blue)and a transparent organic insulating film.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor device characterized by comprising:forming a semiconductor layer over an insulating surface; forming a gateinsulating film on the semiconductor layer; forming a gate electrode onthe gate insulating film; forming a first interlayer insulating film onthe gate electrode; forming a second interlayer insulating film on thefirst interlayer insulating film; forming a first contact hole whichreaches the semiconductor layer and forming a wiring for electricallyconnecting among respective TFTs; forming a third interlayer insulatingfilm to cover the wiring; forming a groove which reaches a substratebetween a region through which light is transmitted and a TFT;continuously forming a light shielding film from a region located overthe third interlayer insulating film to the groove; forming a secondcontact hole for connecting a pixel electrode and the wiring; forming afourth interlayer insulating film on the light shielding film; removinga portion of an insulating film formed in the second contact hole toexpose the wiring; and forming the pixel electrode.

According to the present invention, there is provided a method ofmanufacturing a semiconductor device characterized by comprising:forming a semiconductor layer over an insulating surface; forming a gateinsulating film on the semiconductor layer; forming a gate electrode onthe gate insulating film; forming a first interlayer insulating film onthe gate electrode; forming a second interlayer insulating film on thefirst interlayer insulating film; forming a first contact hole whichreaches the semiconductor layer and forming a wiring for electricallyconnecting among respective TFTs; forming a third interlayer insulatingfilm to cover the wiring; removing a base insulating film, the gateinsulating film, the first interlayer insulating film, and the secondinterlayer insulating film in a region through which light istransmitted to form a window which reaches a substrate; forming an upperlight shielding film on the third interlayer insulating film to cover aTFT; removing a lower light shielding film formed on a bottom surface ofthe window; forming a second contact hole in the upper light shieldingfilm; forming a fourth interlayer insulating film on the upper lightshielding film; filling the window with a transparent insulating filmfor leveling; forming a fifth interlayer insulating film on the upperlight shielding film; removing a portion of an insulating film filledinto the second contact hole to expose the wiring; and forming a pixelelectrode on the fifth interlayer insulating film.

According to the present invention, there is provided a method ofmanufacturing a semiconductor device characterized by comprising:forming a semiconductor layer over an insulating surface; forming a gateinsulating film on the semiconductor layer; forming a gate electrode onthe gate insulating film; forming a first interlayer insulating film onthe gate electrode; forming a second interlayer insulating film on thefirst interlayer insulating film; forming a first contact hole whichreaches the semiconductor layer and forming a wiring for electricallyconnecting among respective, TFTs; forming a third interlayer insulatingfilm to cover the wiring; removing a base insulating film, the gateinsulating film, the first interlayer insulating film, and the secondinterlayer insulating film in a region through which light istransmitted to form a hole which reaches a substrate; forming an upperfirst light shielding film on the third interlayer insulating film tocover a TFT; forming a second contact hole which reaches the wiring inthe upper first light shielding film and the third interlayer insulatingfilm; forming a first insulating film on the upper first light shieldingfilm; removing a portion of the first insulating film filled into thesecond contact hole to expose the wiring; forming an upper second lightshielding film on the first insulating film; forming a second insulatingfilm on the upper second light shielding film; forming an upper thirdlight shielding film on the second insulating film; removing a lowerlight shielding film, the upper first light shielding film, the firstinsulating film, the upper second light shielding film, the secondinsulating film, and the upper third light shielding film, which areformed on a bottom surface of the hole; forming a third contact holewhich reaches the upper second light shielding film in the upper thirdlight shielding film and the second insulating film; forming a fourthinterlayer insulating film; filling the hole with a transparentinsulating film for leveling; forming a fifth interlayer insulating filmon the upper third light shielding film; removing a portion of aninsulating film filled into the third contact hole to expose the uppersecond light shielding film; and forming a pixel electrode on the fifthinterlayer insulating film.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized by comprising forming alower light shielding film on the insulating surface.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized in that a lower lightshielding film, the upper first light shielding film, and the upperthird light shielding film are connected with a wiring having a groundpotential.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized in that a lower lightshielding film is in contact with an upper first light shielding film atthe bottom surface of the window.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized in that a leveling step forthe window is performed using an organic insulating film.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized in that a leveling step forthe window is performed by laminating a photoresist film colored withone of R (red), G (green), and B (blue) and a transparent organicinsulating film.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized in that the semiconductorlayer is crystallized by irradiation of laser light.

Also, according to the present invention, there is provided a method ofmanufacturing a semiconductor characterized in that the semiconductorlayer is a crystalline semiconductor layer obtained by reducing aconcentration of a catalytic element in the semiconductor layer bygettering the catalytic element after crystallization using thecatalytic element.

As described above, according to the present invention, the structure isused in which the TFT is covered with the light shielding film toprevent the occurrence of a photo leak current by light incident intothe semiconductor layer of the TFT without intention, such as diffractedlight or stray light.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A to 1C show examples of semiconductor devices manufacturedaccording to the present invention;

FIGS. 2A to 2C show one example in accordance with an embodiment of thepresent invention;

FIGS. 3A and 3B show one example in accordance with the embodiment ofthe present invention;

FIG. 4 shows one example in accordance with the embodiment of thepresent invention;

FIGS. 5A to 5D show one example in accordance with an embodiment of thepresent invention;

FIGS. 6A to 6D show one example in accordance with the embodiment of thepresent invention;

FIG. 7 shows one example in accordance with an embodiment of the presentinvention;

FIGS. 8A to 8D show one example in accordance with an embodiment of thepresent invention;

FIGS. 9A to 9D show one example in accordance with the embodiment of thepresent invention;

FIGS. 10A to 10D show one example of an electrical appliance;

FIGS. 11A to 11F show examples of electrical appliances;

FIGS. 12A to 12C show examples of electrical appliances;

FIGS. 13A and 13B show examples in accordance with an embodiment of thepresent invention;

FIG. 14 shows one example in accordance with the embodiment of thepresent invention;

FIG. 15 shows one example in accordance with the embodiment of thepresent invention; and

FIGS. 16A and 16B show examples in accordance with an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment Mode 1

A structure of a transmission type liquid crystal display devicemanufactured according to the present invention will be described withreference to FIG. 1A.

A base insulating film 11 is formed on a substrate 10. A TFT composed ofa semiconductor layer 12, a gate insulating film 13, and a gateelectrode 14 is formed on the base insulating film 11.

A first interlayer insulating film 15 and a second interlayer insulatingfilm 16 are formed on the gate electrode 14. The second interlayerinsulating film 16 is leveled if necessary. Subsequently, a wiring 17for electrically connecting among respective TFTs is formed to connectwith the source region or the drain region of the semiconductor layer12. A third interlayer insulating film 18 is formed to cover the wiring17, and then a groove is formed in the boundary between the TFT and anopening portion. The groove is formed so as to reach the substrate.Next, a conductive film is continuously formed from a surface of thethird interlayer insulating film 18 into the groove by a metal CVDmethod to form a light shielding film 19.

Subsequently, a fourth interlayer insulating film 20 is formed and thena pixel electrode 21 is formed so as not to be in contact with the lightshielding film 19.

Note that a storage capacitor 202 is composed of a region 22 extendedfrom the semiconductor layer 12 (one electrode of a storage capacitor),an insulating film 23 which is the same layer as the gate insulatingfilm 13 (dielectric), and a capacitor wiring 24 which is the same layeras the gate electrode 14 (the other electrode of the storage capacitor).

With respect to a structure of a semiconductor device of the presentinvention, each of pixels in a pixel portion has a TFT 201 covered withthe light shielding film 19, which is continuously formed from a regionbetween the TFT 201 and the pixel electrode to the boundary between theTFT 201 and the opening portion (region which is intended to controldisplay). In addition, in a region of each pixel through which light istransmitted, the base insulating film 11, the gate insulating film 13,the first interlayer insulating film 15, the second interlayerinsulating film 16, the third interlayer insulating film 18, and thefourth interlayer insulating film 20 are laminated between the pixelelectrode and the substrate.

In the TFT having the structure shown in FIG. 1A, a light shielding film(lower light shielding film) may be provided between the substrate 10and the semiconductor layer 12. In this case, a depth of the groovefilled with the light shielding film is preferably determined asappropriate by a performer. The depth may be one in which the groovereaches the lower light shielding film or one in which the groove doesnot reach the lower light shielding film.

Embodiment Mode 2

Another structure of a TFT of the present invention will be describedwith reference to FIG. 1B. Note that the same reference symbol is usedin the case where the same member as in shown in FIG. 1A is indicated.

A base insulating film 11 is formed on a substrate 10. A TFT composed ofa semiconductor layer 12, a gate insulating film 13, and a gateelectrode 14 is formed on the base insulating film 11.

A first interlayer insulating film 15 and a second interlayer insulatingfilm 16 are formed on the gate electrode 14. The second interlayerinsulating film 16 is leveled if necessary. Subsequently, a wiring 17for electrically connecting among respective TFTs is formed to connectwith the source region or the drain region of the semiconductor layer12. A third interlayer insulating film 18 is formed to cover the wiring17, and then the third interlayer insulating film 18, the secondinterlayer insulating film 16, the first interlayer insulating film 15,the gate insulating film 13, and the base insulating film 11 in a regionsomewhat wider than the opening portion (region which is intended tocontrol display) are removed. Next, a conductive film is continuouslyformed from a surface of the third interlayer insulating film 18 to theside surface of a region in which the gate insulating film and theinterlayer insulating films are removed (window) to form an upper lightshielding film 19. Next, the upper light shielding film 19 formed on thebottom surface of the window is removed and a fourth interlayerinsulating film 20 is formed. After that, the window is filled with atransparent organic insulating film 30 or the like to be leveled, afifth interlayer insulating film 31 is formed thereon, and a pixelelectrode 32 is formed.

In the TFT of the present invention, the light shielding film is formedto cover and fit the TFT from the bottom surface of the region in whichat least a portion of the gate insulating film and portions of theinterlayer insulating films are removed (window). There is the openingportion inside the window. In this embodiment mode, since an aspectratio of the window is small, even when a sputtering method easier thana metal CVD method is used for manufacturing the upper light shieldingfilm 19, preferable coverage can be obtained.

Also, since the TFT can be covered with the light shielding film, theoccurrence of a photo leak current can be suppressed.

Embodiment Mode 3

Another structure of a TFT of the present invention will be describedwith reference to FIG. 1C.

A lower light shielding film 101 is formed on a substrate 100. A baseinsulating film 102, a semiconductor layer 103, and a gate insulatingfilm 104 are formed in order on the lower light shielding film 101. Agate electrode 105 is formed on the gate insulating film 104 and a firstinterlayer insulating film 107 and a second interlayer insulating film108 are formed on the gate electrode 105. A wiring 109 connected withthe source region or the drain region of the semiconductor layer 103 isformed on the second interlayer insulating film. A third interlayerinsulating film 110 is formed to cover the wiring 109. An upper lightshielding film 111 is provided on the third interlayer insulating film110.

Also, a pixel electrode 114 is formed on the upper light shielding film111 via an insulating film 112. The pixel electrode 114 is connectedwith a wiring connected with the drain region of a TFT, through acontact hole formed in the upper light shielding film 111 and the thirdinterlayer insulating film 110. A storage capacitor 202 is composed of asemiconductor layer 120, an insulating film 121, and a capacitor wiring106. The semiconductor layer 120 is extended from the drain region andbecomes one electrode of the storage capacitor. The insulating film 121which is the same layer as the gate insulating film becomes a dielectricof the storage capacitor. The capacitor wiring 106 formed in the samelayer as the gate electrode becomes the other electrode of the storagecapacitor.

Such a TFT 201 and the storage capacitor 202 are formed in each ofpixels. Note that an opening portion is formed inside the window inwhich the third interlayer insulating film 110, the second interlayerinsulating film 108, the first interlayer insulating film 107, the gateinsulating film 104, and the lower light shielding film 101 are removed.The upper light shielding film is continuously formed from a surface ofthe second interlayer insulating film 108 to the wall surface of thewindow. However, the upper light shielding film formed on the bottomsurface of the window is removed.

The lower light shielding film 101 and the upper light shielding film111 are formed to be in contact with each other at the bottom of thewindow so as to make the same ground potential. Although not shown,these films are connected with a wiring for providing a groundpotential.

Note that the window is filled with an organic insulating film 115 madeof acrylic or the like for leveling. After leveling, an interlayerinsulating film 113 is formed thereon, and a pixel electrode 114 isformed. The pixel electrode 114 is electrically connected with thewiring connected with the drain region of the semiconductor layer 103.The TFT 201 and the pixel electrode 114 are electrically connected witheach other.

As described above, a liquid crystal panel can be manufactured in whichthe upper light shielding film 111 is formed to cover and fit the TFT inthe pixel portion and the TFT is completely light-shielded by the lowerlight shielding film 101 and the upper light shielding film 111.

Embodiment 1

In this embodiment, steps of manufacturing an active matrix substrateaccording to the present invention will be described.

First, in order to form a lower light shielding film 301 on a quartzsubstrate 300, a polysilicon film and a WSix film are laminated. Notethat, with respect to the lower light shielding film 301, a lightshielding property in which a requirement level is satisfied is requiredand a heat resistance to heat treatment for activation of a TFT isessential. Further, since it is preferable that a ground potential isprovided, the lower light shielding film is preferably a conductivefilm. Thus, one kind or plural kinds of films selected from the groupconsisting of a polysilicon film, WSi_(x) (x=2.0 to 2.8) film, and afilm made of a conductive material such as Al, Ta, W, Cr. or Mo may beused as the lower light shielding film (FIG. 2A).

Subsequently, a base insulating film 302 is formed on the lower lightshielding film 301. The base insulating film 302 is obtained by formingan insulating film including silicon (for example, a silicon oxidenitride film, a silicon nitride oxide film, or a silicon nitride film)by an LPCVD method, a plasma CVD method, or a sputtering method. Then,an amorphous semiconductor film (not shown) is formed on the baseinsulating film 302. Although the amorphous semiconductor film is notparticularly limited, it is preferably made of a silicon film, a silicongermanium (Si_(x)Ge_(1−x): 0<x<1, typically, x=0.001 to 0.05) alloy, orthe like. Note that, here, an amorphous silicon film is formed at a filmthickness of 65 nm.

Next, the amorphous silicon film is crystallized. Heat treatment isperformed using a furnace at 600° C. for 24 hours to form a crystallinesilicon film (not shown). Note that a silicon oxide film is formed inthe surface of the silicon film by the crystallization processing. Sincethis film is an extremely thin film which can be removed by etching orthe like, no problem is caused.

Next, the oxide film formed in the surface of the crystalline siliconfilm is removed, and then heat treatment for improving a film quality ofthe semiconductor film is performed before a gate insulating film 304 isformed. Heat treatment is performed for the crystalline silicon film at900° C. to 1050° C. to form an oxide film in the surface of thecrystalline semiconductor film. This silicon oxide film is removed. Heattreatment is preferably performed for the crystalline silicon film toform the silicon oxide film in the surface thereof such that a finalfilm thickness of the crystalline silicon film becomes 30 nm to 50 nm.In this embodiment, the film thickness of the crystalline silicon filmis set to be 35 nm. Subsequently, the obtained crystalline silicon filmis formed in a predetermined shape to form a semiconductor layer 303having an area for a channel forming region, a source region, and adrain region of a TFT and an area for a wiring as one electrode of astorage capacitor.

Next, the gate insulating film 304 is formed on the semiconductor layers(FIG. 2B). Subsequently, an impurity element for providing a p-type(hereinafter referred to as a p-type impurity element) is added to thesemiconductor layer in an area as a p-channel TFT through the gateinsulating film 304. An element belonging to group 13 of the periodictable, typically, boron (B) or gallium (Ga) can be used as the p-typeimpurity element. This step is performed for controlling a thresholdvoltage of the TFT, which is called a channel dope step. The p-typeimpurity element is added to the semiconductor layer at a concentrationof 1×10¹⁵/ cm³ to 1×10¹⁸/cm³ in this step.

Next, a mask made of a resist is formed and an impurity element forproviding an n-type (hereinafter referred to as an n-type impurityelement and phosphorus is used here) is added to the semiconductor layerin portions as the source region and the drain region of an n-channelTFT and one electrode of a storage capacitor to form n-type impurityregions including phosphorus at a high concentration. Phosphorus isincluded in the regions at a concentration of 1×10²⁰/ cm³ to 5×10²¹/cm³.

Next, a gate electrode 305 a and a wiring 305 b as one electrode of thestorage capacitor (hereinafter referred to as a capacitor wiring) areformed, TaN, Ta, Ti, Mo, W, Cr, Si to which an impurity element isadded, or the like can be used as a material for the gate electrode 305a and the capacitor wiring 305 b. Note that plural kinds of films madeof those may be laminated to form the gate electrode.

Next, an n-type impurity element is added to the semiconductor layerusing the gate electrode as a mask. Here, phosphorus is used as then-type impurity element. The regions to which the n-type impurityelement is added are low concentration impurity regions serving as LDDregions of the n-channel TFT. The n-type impurity element is included inthe are low concentration n-type impurity regions at a concentration of1×10¹⁶/cm³ to 5×10¹⁸/cm³.

Next, a region as the n-channel TFT later is covered with a mask andboron as a p-type impurity element is added to the semiconductor layeras the source region or the drain region of the p-channel TFT later toinclude boron at a concentration of 3×10²⁰/cm³ to 5×10²¹/cm³ (notshown).

Next, a silicon nitride film, a silicon oxide nitride film, or a siliconnitride oxide film is formed as a first interlayer insulating film 306at a film thickness of 50 nm to 500 nm by a plasma CVD method.

After that, heat treatment is performed for activating the impurityelement added to the respective semiconductor layers. A method using afurnace, a method using laser light irradiation, a lamp anneal method,or a combination thereof may be performed as the heat treatment method.The activation is conducted in an inert gas atmosphere at 550° C. to1000° C.

Next, hydrogenation is conducted for terminating dangling bonds in thesemiconductor layers by thermally excited hydrogen. Heat treatment isperformed in an atmosphere including hydrogen at 410° C. for 1 hour.Plasma hydrogenation processing using hydrogen excited by plasma may beperformed as another hydrogenation means.

Next, a second interlayer insulating film 307 is formed at a filmthickness of 500 nm to 1000 nm. An organic resin film made of acrylic,polyimide, polyamide. or BCB (benzocyclobutene) or an inorganicinsulating film such as a silicon oxide nitride film, a silicon nitrideoxide film may be used for the second interlayer insulating film 307.Note that, in this embodiment, a silicon oxide nitride film is formed ata film thickness of 900 nm and planarized by a CMP method (FIG. 2C).

Subsequently, first contact holes which reach the semiconductor layers303 are formed and wirings 308 electrically connected with therespective TFTs are formed. A laminate structure in which a conductivefilm including mainly titanium is formed at a film thickness of 50 nm to100 nm and then a conductive film including mainly aluminum is formed ata film thickness of 300 nm to 500 nm. is preferably used for the wirings308. It is necessary to use a material which prevents electrolyticcorrosion when being in contact with a pixel electrode for the top layerwhich is in contact with the pixel electrode.

Next, a third interlayer insulating film 309 is formed. The thirdinterlayer insulating film 309 made from a silicon oxynitride film isformed at a film thickness of 600 nm (FIG. 3A).

Next, in a region substantially corresponding to an opening portion(region which is intended to control display), the interlayer insulatingfilms, the gate insulating film, and the base insulating film which areformed by the steps until here are removed to expose the lower lightshielding film. Note that a region in which the gate insulating film andthe interlayer insulating films are removed (window) is formed to bewider than a region through which light is actually transmitted (openingportion).

Next, an upper light shielding film 311 is formed. A film through whichlight is not transmitted and which has electrical conductivity, here, aconductive film including mainly aluminum is formed as the upper lightshielding film at a film thickness of 100 nm to 200 nm. Note that, sincea ratio of a depth to a width (aspect ratio) in the window before theupper light shielding film is small, even when a sputtering method isused, the conductive film can be formed with a preferable coverage. Theupper light shielding film is formed to be in contact with the lowerlight shielding film and to make the same potential. Although not shown,a wiring for providing a ground potential is connected with the lowerlight shielding film and the upper light shielding film.

Next, the lower light shielding film and the upper light shielding filmwhich are formed on the bottom surface of the window are removed. Also,the upper light shielding film is removed for forming a second contacthole for electrically connecting a drain electrode and a pixelelectrode. In either step, etching is conducted using a pattern made ofa resist as a mask. Note that, since regions to be etched have differentheights and films to be removed have different laminate structures, theremoving steps are separately performed for simplification of steps.Either step may be performed first (FIG. 14).

Subsequently, an insulating film 312 made from a silicon nitride film, asilicon oxide nitride film, a silicon nitride oxide film, or the like isformed on the upper light shielding film 311 by a plasma CVD method andthen the window is filled with an organic insulating film 313 made ofacrylic or the like for leveling (FIG. 3B).

Note that the window may be filled with a photoresist film colored withR. G. and B and then an organic resin film made of acrylic or the likemay be formed. When the colored layer is used for leveling the window, aproblem with respect to a color shift caused in the case where thecolored layer is provided in a counter substrate side can be solved.

Subsequently, a fourth interlayer insulating film 314 made from asilicon nitride film, a silicon oxide nitride film, a silicon nitrideoxide film, or the like is formed by a sputtering method. A portion ofthe insulating film with which the contact hole has been filled isremoved to expose the drain electrode and then a pixel electrode 315 isformed. At this time, it is important to remove the insulating film suchthat the upper light shielding film 311 is not in contact with a pixelelectrode 315. Note that, since a transmission liquid crystal displaydevice is manufactured in this embodiment, a transparent ITO film(compound of indium oxide and tin oxide) is formed as the pixelelectrode at a film thickness of 100 nm by sputtering method (FIGS. 4and 15). Note that, when a metallic film having a light shieldingproperty, for example, a pixel electrode in which Al or a conductivematerial is plated with Ag is formed in stead of the ITO film, areflection liquid crystal display device can be obtained. Also, theupper light shielding film formed on the bottom surface of the windowmay be used as a reflecting plate without removing it. In this case,liquid crystal is controlled by the transparent pixel electrode formedon a leveling film and a counter electrode.

By such steps, the following active matrix substrate can bemanufactured. That is, the active matrix substrate has on the substratea TFT 320 which is covered with the lower light shielding film and theupper light shielding film and composed of the base insulating film, thesemiconductor layer, the gate insulating film, and the gate electrodeand a storage capacitor 321 which is composed of the semiconductor layeras one electrode, the insulating film which is the same layer as thegate insulating film as a dielectric, and a capacitor wiring made fromthe same layer as the gate electrode. A ratio of a region through whichlight is transmitted to a pixel area (aperture ratio) exceeds 50%.

Also, an orientation film for orienting the liquid crystal layer isformed in the thus obtained active matrix substrate, a counter substratein which a counter electrode and an orientation film are formed and theactive matrix substrate are bonded using a known cell assemblytechnique, and liquid crystal is injected therebetween. Therefore, anactive matrix liquid crystal display device can be completed.

Embodiment 2

In this embodiment, a method of forming a plurality of upper lightshielding films to form a storage capacitor along a wall surface of aregion in which at least a portion of a gate insulating film and aportion of an interlayer insulating film are removed (window) will bedescribed.

Based on the manufacturing steps indicated in Embodiment 1 the statethat the lower light shielding film on the bottom surface of the windowshown in FIG. 3A is exposed is obtained (FIG. 5A).

Next, an upper first light shielding film 401 is formed. A conductivefilm (conductive film including mainly an element selected from thegroup consisting of aluminum, chromium, and titanium) is formed as theupper first light shielding film 401 at a film thickness of 100 nm to200 nm. Subsequently, second contact holes which reach the wirings 308are formed in the upper first light shielding film 401 and the thirdinterlayer insulating film 309. Note that the first contact holes arecontact holes for connecting the wirings and the semiconductor layers.

Next, a first insulating film 402 made from a silicon oxide nitridefilm, a silicon nitride oxide film, a silicon nitride film, or the likeis formed on the upper first light shielding film 401 by a plasma CVDmethod or the like.

Next, a portion of the first insulating film filled into the secondcontact holes is removed to expose the upper first light shielding film401, and then an upper second light shielding film 403 is formed on thefirst insulating film 402. Note that, since the upper second lightshielding film 403 is to be connected with a pixel electrode, it isformed by, for example, laminating a conductive film made of a materialwhich prevents electrolytic corrosion by contact with an ITO film usedas the pixel electrode. In this embodiment, a structure is used suchthat a conductive film including mainly aluminum is formed and then aconductive film including mainly tungsten is laminated in a pixelelectrode contact side. The film thickness of the upper second lightshielding film 403 is set to be 100 nm to 200 nm. Subsequently, a secondinsulating film 404 is formed on the upper second light shielding film403 as in the case of the first insulating film.

Next, an upper third light shielding film 405 is formed on the secondinsulating film 404. Note that the upper third light shielding film iselectrically connected with the lower light shielding film 301 or theupper first light shielding film 401 so as to provide the same potential(ground potential in this embodiment) as the lower light shielding film301 and the upper first light shielding film 401. Note that a wiring ispreferably connected therewith so as to provide a ground potential byconnection in a region except for a pixel, in which a problem such as anaperture ratio is reduced by connection is not caused.

Next, third contact holes for electrically connecting a pixel electrodewhich is formed later and the upper second light shielding film 403 areformed. The lower light shielding film 301, the upper first lightshielding film 401, the upper second light shielding film 403, and theupper third light shielding film 405 on the bottom surface of the windoware removed.

Next, a fourth interlayer insulating film 406 is formed on the upperthird light shielding film 405. Note that an insulating film which isformed by a plasma CVD method and selected from a silicon nitride film,a silicon oxide nitride film, a silicon nitride oxide film, and the likemay be also used as the fourth interlayer insulating film 406 as in thecases of the first insulating film 402 and the second insulating film404.

Next, leveling for the window is conducted. An organic insulating filmmade of acrylic or the like is preferably used as a leveling film 407 asin Embodiment 1. Also, as indicated in Embodiment 1, the window isfilled with a photoresist film colored with R, G, or B and then levelingmay be conducted using an organic resin film made of acrylic or thelike.

Subsequently, a fifth interlayer insulating film 408 made from a siliconnitride film, a silicon oxide nitride film, a silicon nitride oxidefilm, or the like is formed on the entire surface by a sputtering methodand a portion of the insulating film filled into the third contact holesis removed to expose the upper second light shielding film 403. Then, apixel electrode 409 is formed so as not to be in contact with the uppersecond light shielding film 403. A transparent ITO film (compound ofindium oxide and tin oxide) is formed as the pixel electrode 409 at afilm thickness of 100 nm by a sputtering method.

By the above steps, a first storage capacitor 502 and a second storagecapacitor 503 are formed along a side surface of the window. In thefirst storage capacitor 502, the upper first light shielding film 401 isone capacitor wiring, the first insulating film 402 is a dielectric, andthe upper second light shielding film 403 is the other capacitor wiring.Also, in the second storage capacitor 503, the upper second lightshielding film 403 is one capacitor wiring, the second insulating film404 is a dielectric, and the upper third light shielding film 405 is theother capacitor wiring. Note that, although a sufficient capacitance isobtained by the first storage capacitor and the second storagecapacitor, the storage capacitor composed of the semiconductor layer,the insulating film which is the same layer as the gate insulating film,and the capacitor wiring which is the same layer as the gate electrode,as in the Embodiment 1 may be formed together with these capacitors.

In order to further increase the capacitance of the storage capacitorelement, a portion of the lower light shielding film formed on thebottom surface of the window is removed and then the exposed substrateis cut. Thus, the storage capacitor element may be extended to the innerportion of the substrate.

The wiring 308 and the upper second light shielding film 403 areconnected with each other and the upper second light shielding film 403and the pixel electrode 409 are connected with each other. Finally, thepixel electrode 409 and the wiring 308 are electrically connected witheach other. Thus, a TFT 501 can be formed as a switching element of apixel. Also, when the two-stage connection between the wiring and thepixel electrode via the upper light shielding film is made as in thisembodiment, an aspect ratio of contact holes can be reduced. Thus,processing is easy and a preferable coverage can be obtained even when asputtering method is used at film formation. Further, a contactresistance can be reduced as compared with the case where a contact holeis narrow and long. Furthermore, if the position of the contact hole forthe pixel electrode (ITO) and the upper second light shielding film isshifted from that of the contact hole for the upper second lightshielding film and the wiring, a light shielding property is improvedand a problem that a leak current is caused by photo excitation can besolved.

As described above, when the plurality of upper light shielding filmsare formed to cover the TFT, the TFT can be completely shielded and thestorage capacitor having a sufficient capacitance can be formed alongthe side surface of the window. Thus, an aperture ratio can be furtherincreased.

Embodiment 3

In this embodiment, one example of an active matrix liquid-crystaldisplay device manufactured using the active matrix substratemanufactured in Embodiment 1 or 2 will be described.

In FIG. 7, an active matrix substrate includes a pixel portion, drivercircuits, and another signal processing circuit, which are formed on asubstrate. A TFT (also called a pixel TFT) and a storage capacitor areformed in the pixel portion. The driver circuits formed in the vicinityof the pixel portion are fundamentally composed of CMOS circuits.

A gate line and a source line are formed to extend them from the drivercircuits to the pixel portion and connected with the pixel TFT. An FPC(flexible printed circuit board) is connected with an external inputterminal and used for inputting an image signal and the like to thedriver circuits. Note that the FPC is strongly bonded through areinforcement resin to the substrate and connected with the respectivedriver circuits through connection wirings. Although not shown, acounter electrode is formed in a counter substrate.

According to the active matrix liquid crystal display device formed bythe present invention, the light shielding film is formed on the TFT toover it. Thus, the occurrence of a photo leak current by stray light canbe suppressed, a potential of the pixel electrode is not varied, and ahigh quality display can be conducted.

Embodiment 4

A pixel having another structure according to the present invention willbe described with reference to FIGS. 13A and 13B.

In accordance with the steps in Embodiment 1, the steps until the secondinterlayer insulating film 16 is formed are performed. Subsequently, inthe step of forming the first contact hole which reaches thesemiconductor layer, grooves are formed in the boundary between a regionthrough which light is transmitted and the TFT and wirings 50 forelectrically connecting among the respective TFTs are formed. Thewirings are continuously formed so as to fill the grooves therewith froma region over the second interlayer insulating film.

Subsequently, the third interlayer insulating film 18 is formed and theupper light shielding film 19 is formed. Then, a second contact hole forconnecting a pixel electrode and the wiring are formed and the fourthinterlayer insulating film 20 is formed. A portion of an insulating filmfilled into the second contact hole is removed to such an extent thatthe light shielding film is not in contact with the pixel electrode, andthen the pixel electrode 21 is formed.

Another example is shown in FIG. 13B. In accordance with the steps inEmbodiment 1, the steps until the second interlayer insulating film 16is formed are performed. Subsequently, a contact hole which reaches asemiconductor layer is formed and the base insulating film 11, the gateinsulating film 13, the first interlayer insulating film 15, and thesecond interlayer insulating film 16 in a region somewhat wider than anopening portion are removed to form a window.

Subsequently a wiring for electrically connecting among respective TFTsis formed. The wiring is continuously formed from a region located onthe second interlayer insulating film 16 along the wall surface of thewindow. The wiring formed on the bottom surface of the window isremoved, and then the third interlayer insulating film 18 is formed andthe light shielding film 19 is formed. Next, the fourth interlayerinsulating film 20 is formed, and then a leveling film 30 for the windowis formed and the fifth interlayer insulating film 31 is formed. Afterthat, a portion of an insulating film filled into a second contact holeis removed to such an extent that the light shielding film is not incontact with the pixel electrode, and then the pixel electrode 32 isformed.

As described above, even when the wiring and the light shielding filmare used, the semiconductor layer of the TFT can be light-shielded.

Embodiment 5

In this embodiment, steps of forming a crystalline semiconductor layerwill be described.

A lower light shielding film 1201 and a base insulating film 1202 areformed on a substrate 1200. Then, an amorphous silicon film 1203 isformed as an amorphous semiconductor film on the base insulating film1202. Then, a mask, 1204 is formed on the amorphous silicon film 1203, ametallic element having a function for promoting crystallization(hereinafter referred to as a catalytic element) is added onto theamorphous silicon film exposed from opening portions of the mask to forma catalyst-containing layer 1205. A metallic element such as Ni, Fe. Co,Ru, Rh, Pd, Os, Pt, or Au can be used as the catalytic element. In thisembodiment, nickel (Ni) is used as the catalytic element (FIG. 8A).

Subsequently, heat treatment is performed in a nitrogen atmosphere at600° C. (500° C. to 700° C.) for 12 hours (4 hours to 12 hours) to forma crystalline silicon film 1206 (FIG. 8B) with an oxide film 1207. Notethat, in order to reduce hydrogen included in the amorphous siliconfilm, heat treatment at 450° C. for 1 hour may be performed aspretreatment to the heat treatment for crystallization. Also, after theheat treatment for crystallization, laser light irradiation may beperformed to improve the crystallinity of the crystalline silicon film(FIG. 8C).

Next, heat treatment for reducing a concentration of the catalyticelement included in the crystalline silicon film is performed. Becauseit is considered that the catalytic element is segregated in a grainboundary of the silicon film and the segregation becomes a leak path ofa very weak current, and thus an off current (current when a TFT is inan off state) is suddenly increased.

First, a mask 1208 is formed on the crystalline silicon film and anelement belonging to group 15 of the periodic table (typically,phosphorus) is added to the crystalline silicon film. Gettering sites1209 including phosphorus at a concentration of 1×10¹⁹/cm to 1×10²⁰/cm³are formed in the crystalline silicon film exposed from the mask openingportions. Note that regions to which the element belonging to group 15of the periodic table is added and the catalytic element is moved by theheat treatment in this specification is called the gettering sites.

Next, heat treatment is performed in a nitrogen atmosphere at 450° C. to650° C. for 4 hours to 12 hours. The catalytic element in thecrystalline silicon film is moved to the gettering sites by the heattreatment. Thus, the concentration of the catalytic element in thecrystalline silicon film can be reduced to be 1×10¹⁷/cm ³ or lower,preferably, 1×10¹⁶/cm³ or lower.

Therefore, the crystalline silicon film obtained using the catalyticelement has a crystal structure in which rod-shaped crystal or acolumn-shaped crystal is oriented with a specific directional propertyand the crystallinity is very high. When such a semiconductor layer isused, a TFT having a preferable characteristic can be manufactured. Notethat this embodiment can be used by being combined with Embodiments 1and 2.

Embodiment 6

In this embodiment, a manufacturing step of crystalline semiconductorlayer is described.

A lower light shielding film 1101 and a ground insulating film 1102 areformed on the substrate 1100. Next, an amorphous silicon film 1103 isformed to 200 nm thick on the ground insulating film 1102. Then, acatalyst element is added to the amorphous silicon film. In thisembodiment, nickel is used as a catalyst element and an aqueous solutioncontaining Ni (10 ppm by weight) (aqueous solution of nickel acetate) isapplied to the film by a spin-coating method to form a catalyst elementcontent layer 1104. Sputtering and evaporation may be used other thanspin-coating in adding a catalyst element. (FIG. 9A)

Next, prior to a crystallizing step, a heating process is carried outfor around one hour at 400 to 500° C. to eliminate hydrogen from thefilm, and then, another heating process is carried out for 4 to 12 hoursat 500 to 650° C. to perform a process for crystallizing thesemiconductor film so that a crystal silicon film 1105 would be formed.(FIG. 9B) In addition, laser light can be irradiated to improve acrystallinity. (FIG. 9C)

A step for reducing the concentration of a catalyst element remainingon, the crystal silicon film 1105 is carried out. It is assumed that thecrystal silicon film 1105 contains a catalyst element at theconcentration of 1×10¹⁹cm³ or more. It is possible to use the crystalsilicon film 1105 on which the catalyst element remains to manufacture aTFT, but in this case, there is a problem that the catalyst element issegregated in a defect of a semiconductor layer and an OFF-state currentunexpectedly rises. Accordingly, a heating process is carried out forthe purpose of eliminating the catalyst element from the crystal siliconfilm 1105 SO that the concentration would be reduced to 1×10¹⁷/cm³ orless, preferably 1×10¹⁶/cm³ or less.

A barrier layer 1106 is formed on the surface of the crystal siliconfilm 1 105. The barrier layer 1106 is provided so that the crystalsilicon film 1105 would not be etched in eliminating by etching agettering site 1107 provided later on the barrier layer 1106.

The thickness of the barrier layer 1106 is around 1 to 10 nm, and thebarrier layer 1106 may be easily a chemical oxide formed by processingthe crystal silicon film with ozone water. In another example, thechemical oxide can be formed similarly by means of a solution in whichsulfuric acid, hydrochloride acid or nitric acid is mixed with asolution of hydrogen peroxide. In another example, the barrier layer maybe formed by carrying out a plasma process in an oxide atmosphere orultraviolet rays radiation in an oxygen content atmosphere so that ozonewould be generated to perform an oxidation process. Further, in anotherexample, the barrier layer can be formed by a thin oxide film, which isformed by heating at 200 to 350° C. in a clean oven.

Next, the gettering site 1107 is formed on the barrier layer 1106 bysputtering. The gettering site 1107 is formed by means of asemiconductor film containing diluted gas at the concentration of1×10²⁰/cm³ or more, represented by an amorphous silicon film, which is25 to 250 nm in thickness. The gettering site 1107 has preferably a lowdensity so that a selecting rate of etching to the crystal silicon film1105 would be large since the gettering site 1107 is eliminated byetching after the gettering step is completed.

The gettering site 1107 is formed by sputtering under a condition thatAr is 50 sccm, film forming power is 3 kW, temperature of a substrate is150° C. and film forming pressure is 0.2 to 1.0 Pa. In accordance withthe above process, the gettering site 1107 containing a diluted gaselement at the concentration of 1×10¹⁹ to 1×10²²/cm³ can be formed. Thediluted gas element does not badly influence the crystal silicon film1105 since it is inert in a semiconductor film, and therefore, thegettering can be performed.

A heating process for ensuring completion of gettering is carried outfollowing to the above. The heating process may be performed by a methodfor heating by means of a furnace or an RTA method in which a lamp orheated Ras is used as a heat source. In the case of using a furnace, theheating process should be performed in a nitrogen atmosphere at 450 to600° C. for 0.5 to 12 hours. In the case of the RTA method, asemiconductor film should be heated to around 600 to 1000° C. at amoment.

The catalyst element remaining on the crystal silicon film 1105 istransported to the gettering site 1107 in such heating process, so thatthe concentration of the catalyst element on the crystal silicon film1105 can be reduced to 1×10¹⁷/cm³ or less, preferably 1×10¹⁶/cm³ orless. The gettering site 1107 is not crystallized in the heating processfor gettering. It may be because the diluted gas element is not effusedand remains in the gettering site even during the heating process.

The getting site 1107 is eliminated by etching after the getteringprocess is completed. Dry etching by means of CIF₃ in which plasma isnot used or wet etching in which an alkaline solution such as a solutioncontaining hydrazine or tetraethyl ammonium hydroxide ((CH₃)₄NOH) isused can be carried out for the above-mentioned etching. In this etchingstep, the barrier layer 1106 works as an etching stopper for preventingthe crystal silicon film 1105 from being etched. The barrier 1106 can beeliminated by means of hydrofluoric acid after the elimination of thegettering site 1107 by etching is completed.

Thus, the crystal silicon film 1105 has a crystal structure in whichcylinder shape or columnar shape crystals are lined up with a specificdirectionality and have a good crystallinity. Further, the concentrationof the catalytic element remaining in the crystal silicon film can bereduced enough. Using such semiconductor film, a good characteristic TFTcan be formed. This embodiment can be implemented by freely combinedwith Embodiments 1 and 2.

Embodiment 7

A method of manufacturing a light emitting device by forming a filmincluding an organic compound (which is called an organic compoundlayer) in which light emission is produced by applying an electric fieldthereto and a cathode on the pixel electrode in the TFT substrateaccording to the present invention will be described by using FIGS. 16Aand 16B.

Based on Embodiment 1, a TFT for controlling a current flowing into alight emitting element (laminate composed of an anode, an organiccompound layer, and a cathode) (current control TFT) is formed on asubstrate, a window 310 is formed, and the upper light shielding film311 and the insulating film 312 are formed. Then, leveling is conductedby filling the window 310 with the organic insulating film 313. Notethat a p-channel TFT is preferably applied to the current control TFT inthis embodiment.

Then, a step between the insulating film 312 and the organic insulatingfilm 313 is reduced for leveling by using the fourth interlayerinsulating film 314, and then a pixel electrode (which is also calledthe anode) 700 is formed to obtain the state as shown in FIG. 3B. Notethat the step between the insulating film 312 and the organic insulatingfilm 313 is not necessarily reduced for leveling. Thus, leveling isconducted as appropriate by a manufacturer if necessary. Next, after thepixel electrode (anode) 700 is formed, a bank 701 made from an organicresin film is formed to cover end portions of the anode 700. When theorganic resin film is formed, since there is no case where the organiccompound layer is formed in the end portion of the anode, theconcentration of an electric field to the organic compound layer can beprevented. Next, the organic resin film formed in a region through whichlight is transmitted is removed to expose the anode 700, an insulatingfilm 702 is formed on the anode 700, and an organic compound layer 703and a cathode 704 are formed on the insulating film.

An organic resin film made of polyimide, polyamide, polyimide amide, orthe like is preferably formed as the insulating film 702 at a filmthickness of 1 nm to 5 nm by a spin coat method, an evaporation method,a sputtering method, or the like.

The organic compound layer 703 is preferably formed by laminating aplurality of layers such as a hole injection layer, a hole transportlayer, a hole blocking layer, an electron transport layer, an electroninjection layer, and a buffer layer in combination in addition to alight emitting layer. It is preferable that the film thickness of theorganic compound layer 703 is about 10 nm to 400 nm.

The cathode 704 is formed by an evaporation method after the formationof the organic compound layer 703. In addition to MgAg or an Al—Li alloy(alloy of aluminum and lithium), a film formed by coevaporation of anelement belonging to group 1 or 2 of the periodic table and aluminum maybe used for the cathode 704. Note that the film thickness of the cathode704 is preferably about 80 nm to 200 nm. Thus, a light emitting deviceas shown in FIG. 16A can be manufactured.

Note that, after the insulating film 312 is formed based on Embodiment1, an anode 1700, an insulating film 1701, an organic compound layer1702, and a cathode 1703 can be also formed in the inner portion of thewindow as shown in FIG. 16B without leveling for the window 310.Therefore, since it is unnecessary to form the bank for preventing theformation of the organic compound layer in the end portions of theanode, a manufacturing cost can be reduced.

Also, when a glass substrate in a region corresponding to the openingportion formed in the window 310 is cut out to be thinner than otherregions, a light emitting region of the light emitting element isexpanded. Thus, the brightness in the light emitting device can be alsoincreased.

Thus, an application area of the present invention is wide and thepresent invention can be also applied to a device except a liquidcrystal display device. Note that a light emitting device can bemanufactured by combining this embodiment with Embodiment Modes 1 to 3and Embodiments 1, 2 and 4 to 6.

Embodiment 8

Electronic equipments, which can display high luminance and high qualityimage, can be realized by incorporating active matrix type liquidcrystal display device (liquid crystal display device or EL displaydevice) by implementing the present invention.

As such electronic apparatus, there are pointed out a projector, a videocamera, a digital camera, a head mount display (goggle type display), apersonal computer, a portable information terminal (mobile computer,portable telephone or electronic book) and the like. Examples of theseare shown in FIGS. 10A–10D, 11A–11F and 12A–12C.

FIG. 10A shows a front type projector including a projection apparatus2601 and a screen 2602.

FIG. 10B shows a rear type projector including a main body 2701, aprojection apparatus 2702, a mirror 2703 and a screen 2704.

Further, FIG. 10C is a view showing an example of a structure of theprojection apparatus 2601 and 2702 in FIG. 10A and FIG. 10B. Theprojection apparatus 2601 or 2702 is constituted by a light sourceoptical system 2801, mirrors 2802, 2804–2806, a dichroic mirror 2803, aprism 2807, a liquid crystal display apparatus 2808, a phase differenceplate 2809 and a projection optical system 2810. The projection opticalsystem 2810 is constituted by an optical system including a projectionlens. Although the embodiment shows an example of three plates type, theembodiment is not particularly limited thereto but may be of, forexample, a single plate type. Further, person of executing theembodiment may pertinently provide an optical system such as an opticallens, a film having a polarization function, a film for adjusting aphase difference or an IR film in an optical path shown by arrow marksin FIG. 10C.

Further, FIG. 10D is a view showing an example of a structure of thelight source optical system 2801 in FIG. 10C. According to theembodiment, the light source optical system 2801 is constituted by areflector 2811, a light source 2812, lens arrays 2813 and 2814, apolarization conversion element 2815 and a focusing lens 2816. Further,the light source optical system shown in FIG. 10D is only an example andthe embodiment is not particularly limited thereto. For example, aperson of executing the embodiment may pertinently provide an opticalsystem such as an optical lens, a film having a polarization function, afilm for adjusting a phase difference or an IR film in the light sourceoptical system.

FIG. 11A shows a personal computer including a main body 2001, an imageinput portion 2002, a display portion 2003 and a keyboard 2004.

FIG. 11B shows a video camera including a main body 2101, a displayportion 2102, a voice input portion 2103, operation switches 2104, abattery 2105 and an image receiving portion 2106.

FIG. 11C shows a mobile computer including a main body 2201, a cameraportion 2202, an image receiving portion 2203, an operation switch 2204and a display portion 2205.

FIG. 11D shows a goggle type display including a main body 2301, adisplay portion 2302 and an arm portion 2303.

FIG. 11E shows a player using a record medium recorded with programs(hereinafter, referred to as record medium) including a main body 2401,a display portion 2402, a speaker portion 2403, a record medium 2404 andan operation switch 2405. The player uses DVD (digital Versatile Disc)or CD as the record medium and can enjoy music, enjoy movie and carryout game or Internet.

FIG. 11F shows a digital camera including a main body 2501, a displayportion 2502, an eye contact portion 2503, operation switches 2504 andan image receiving portion (not illustrated).

FIG. 12A shows a portable telephone including a display panel 3001, anoperation panel 3002. The display panel 3001 and the operation panel3002 are connected to each other in the connecting portion 3003. In theconnecting panel 3003, the angle θ of a face, which is provided thedisplay portion 3004 of the display panel 3001, and a face, which isprovided the operation key 3006 of the operation panel 3002, can bechanged arbitrary. Further, a voice output portion 3005, an operationkey 3006, a power source switch 3007 and a sound input portion 3008 arealso included.

FIG. 12B shows a portable book (electronic book) including a main body3101, display portions 3102 and 3103, a record medium 3104, an operationswitch 3105 and an antenna 3106.

FIG. 12C shows a display including a main body 3201, a support base 3202and a display portion 3203.

As has been described, the range of applying the invention is extremelywide and is applicable to electronic apparatus of all the fields. Theelectronic apparatus of the present invention can be implemented byfreely combined with Embodiments 1 to 4.

According to the present invention, when the light shielding film isformed to cover the TFT, the TFT can be completely covered with thelower light shielding film and the upper light shielding film. Thus, aphoto leak current can be suppressed. Also, a sufficient capacitance canbe obtained without reducing an aperture ratio.

When such a light shielding technique of the TFT is used, a displaydevice capable of displaying an image at a high quality, highdefinition, and high brightness can be realized. Also, when such adisplay device is used for a display unit of an electrical appliance, anelectrical appliance capable of displaying an image at a high quality,high definition, and high brightness can be realized.

1. A light emitting device comprising: a thin film transistor formedover a substrate, the thin film transistor having at least asemiconductor layer and a gate electrode with a gate insulating filminterposed therebetween; a first insulating film formed over the thinfilm transistor; a second insulating film formed over the firstinsulating film and inside an opening portion formed by removing aportion of the first insulating film; a pair of wirings electricallyconnected to the semiconductor layer; and an organic compound layerformed between an anode and a cathode, wherein a portion of the organiccompound layer is formed inside the opening portion.
 2. A light emittingdevice according to claim 1, wherein the anode is in contact with one ofthe pair of the wirings.
 3. A light emitting device according to claim1, wherein the cathode comprises at least one of MgAg and Al—Li alloy.4. A light emitting device according to claim 1, further comprising aninsulating film between the anode and the organic compound layer.
 5. Alight emitting device according to claim 1, wherein the light emittingdevice is an EL display device.
 6. A light emitting device according toclaim 1, wherein the light emitting device is incorporated in at leastone selected from the group consisting of a projector, a personalcomputer, a video camera, a mobile computer, a goggle type display, aplayer using a record medium, a digital camera, a portable telephone,and a portable electronic book.
 7. A light emitting device comprising: athin film transistor formed over a substrate, the thin film transistorhaving at least a semiconductor layer and a gate electrode with a gateinsulating film interposed therebetween; a first insulating film formedover the thin film transistor; a second insulating film formed over thefirst insulating film and inside an opening portion formed by removing aportion of the first insulating film, wherein a side wall of the openingportion has a tapered cross section; a pair of wirings electricallyconnected to the semiconductor layer; and an organic compound layerformed between an anode and a cathode, wherein a portion of the organiccompound layer is formed inside the opening portion.
 8. A light emittingdevice according to claim 7, wherein the anode is in contact with one ofthe pair of the wirings.
 9. A light emitting device according to claim7, wherein the cathode comprises at least one of MgAg and Al—Li alloy.10. A light emitting device according to claim 7, further comprising aninsulating film between the anode and the organic compound layer.
 11. Alight emitting device according to claim 7, wherein the light emittingdevice is an EL display device.
 12. A light emitting device according toclaim 7, wherein the light emitting device is incorporated in at leastone selected from the group consisting of a projector, a personalcomputer, a video camera, a mobile computer, a goggle type display, aplayer using a record medium, a digital camera, a portable telephone,and a portable electronic book.
 13. A light emitting device comprising:a thin film transistor formed over a substrate, the thin film transistorhaving at least a semiconductor layer and a gate electrode with a gateinsulating film interposed therebetween; a first insulating film formedover the thin film transistor; a second insulating film formed over thefirst insulating film, and inside an opening portion formed by removinga portion of the first insulating film, wherein a side wall of theopening portion has a tapered cross section, and wherein a portion ofthe second insulating film is in contact with the substrate; a pair ofwirings electrically connected to the semiconductor layer; and anorganic compound layer formed between an anode and a cathode, wherein aportion of the organic compound layer is formed inside the openingportion.
 14. A light emitting device according to claim 13, wherein theanode is in contact with one of the pair of the wirings.
 15. A lightemitting device according to claim 13, wherein the cathode comprises atleast one of MgAg and Al—Li alloy.
 16. A light emitting device accordingto claim 13, further comprising an insulating film between the anode andthe organic compound layer.
 17. A light emitting device according toclaim 13, wherein the light emitting device is an EL display device. 18.A light emitting device according to claim 13, wherein the lightemitting device is incorporated in at least one selected from the groupconsisting of a projector, a personal computer, a video camera, a mobilecomputer, a goggle type display, a player using a record medium, adigital camera, a portable telephone, and a portable electronic book.19. A light emitting device comprising: a thin film transistor formedover a substrate, the thin film transistor having at least asemiconductor layer and a gate electrode with a gate insulating filminterposed therebetween; a first insulating film formed over the thinfilm transistor; a second insulating film formed over the firstinsulating film and inside an opening portion formed by removing aportion of the first insulating film, wherein the opening portion isformed adjacent to a substrate with the second insulating layerinterposed therebetween; and an organic compound layer formed between ananode and a cathode, wherein a portion of the organic compound layer isformed inside the opening portion.
 20. A light emitting device accordingto claim 19, wherein the cathode comprises at least one of MgAg andAl—Li alloy.
 21. A light emitting device according to claim 19, furthercomprising an insulating film between the anode and the organic compoundlayer.
 22. A light emitting device according to claim 19, wherein thelight emitting device is an EL display device.
 23. A light emittingdevice according to claim 19, wherein the light emitting device isincorporated in at least one selected from the group consisting of aprojector, a personal computer, a video camera, a mobile computer, agoggle type display, a player using a record medium, a digital camera, aportable telephone, and a portable electronic book.
 24. A light emittingdevice comprising: a thin film transistor formed over a substrate, thethin film transistor having at least a semiconductor layer and a gateelectrode with a gate insulating film interposed therebetween; a firstinsulating film formed over the thin film transistor; a secondinsulating film formed over the first insulating film and inside anopening portion formed by removing a portion of the first insulatingfilm, wherein a portion of the second insulating film is in contact withthe substrate; and an organic compound layer formed between an anode anda cathode, wherein a portion of the organic compound layer is formedinside the opening portion.
 25. A light emitting device according toclaim 24, wherein the cathode comprises at least one of MgAg and Al—Lialloy.
 26. A light emitting device according to claim 24, furthercomprising an insulating film between the anode and the organic compoundlayer.
 27. A light emitting device according to claim 24, wherein thelight emitting device is an EL display device.
 28. A light emittingdevice according to claim 24, wherein the light emitting device isincorporated in at least one selected from the group consisting of aprojector, a personal computer, a video camera, a mobile computer, agoggle type display, a player using a record medium, a digital camera, aportable telephone, and a portable electronic book.